bbPress 2: Close forums to new topics, but allow replies to existing topics

I am wondering if there is a way with bbPress 2 to close forums to new topics, but allow users to reply to existing forum topics within that forum (or subforum). Ideally this would emulate the functionality of this bbPress standalone plugin:

I installed “bbPress Topics for Posts” (plugin link).
I wanted to create one forum that collects comments on articles (this plugin does that very well – only downside is that comments made in the forum do not count as comments but are visible).

Anyhow; I want users to be able to reply, but NOT create new topics.
Right now it’s either no new topics and no new replies, OR new topics and new replies.

Of course I could modify the forum.php and remove the for the specific forum. Is there an easier (more future proof) way?